This invention relates to the reduction in thermal stresses in machine components which are subjected to sudden temperature variations and which thermal stresses can cause failure of the component. The invention can find particular use in components of pumps for pumping hot fluids and the like.
In the usual centrifugal pump, there is a space or cavity behind the impeller into which product fluid can pass to the system. Common practice is to use one or more mechanical seals encircling the shaft which connects the pump impeller and its driving means, such as an electric motor. On the impeller side of the mechanical seal, cold fluid, such as cold water, is injected into the system to flow through a gap between the pump housing and the drive shaft. This cold fluid flows into the space or cavity behind the impeller and then into the discharge from the impeller. The cold fluid provides a cooling media for the shaft. At times, pressure pulsations in the space or cavity behind the impeller cause periodic flow reversal, i.e., hot product fluid flowing toward the mechanical seal through the gap between the housing and the drive shaft. Because of the sudden temperature variations due to the aforesaid operating conditions, thermal stresses are induced into the drive shaft which could cause failure of the shaft and a shut-down of the equipment. To protect or shield the drive shaft from such thermal stresses, one or more sleeves encircling the shaft are used. However, these sleeves are also subjected to thermal stresses in the same manner as the shaft itself, and are thus subject to failure, requiring a shut down of the equipment for a part replacement.